AN1058 Freescale Semiconductor / Motorola, AN1058 Datasheet - Page 15

• Manufacturer Part Number: AN1058
• Description: Reducing A/D Errors in Microcontroller Applications
• Manufacturer: Freescale Semiconductor / Motorola

V
Terminal Noise
AN1058
MOTOROLA
DD
/V
SS
and Input
NOTE:
The differential comparator used in the M68HC11 ADC derives its power
from V
(see
performance, is a source of noise, partially due to the wave shape and
harmonics associated with square waves. In addition, the complex
relationship between the primary M68HC11 clock and related noise
voltages are further complicated by dependence of the M68HC11 upon
many software combinations, each sufficiently changing the noise
characteristics emanating from the M68HC11. Therefore, ADC
performance degradation, which is linked to noise generated on
V
specific software combinations. As established earlier, this is due to the
ADC wide bandwidth comparator.
Because the M68HC11 ADC uses a very wide bandwidth comparator
capable of responding to noise components in excess of 20 MHz, it must
be guarded against unwanted noise at its input terminals and V
pins.
DD
Freescale Semiconductor, Inc.
/V
V
In
For More Information On This Product,
Figure
SS
DD
by the M68HC11, can often appear related to execution of
and V
Go to: www.freescale.com
7). The M68HC11, when considered with respect to ADC
V
Figure 7. M68HC11 ADC in Sample Mode
RH
1
1/2
SS
, the power pins that supply the rest of the M68HC11
1
2
4
8
C
S
1.1
1
2
4
A Specific MCU with ADC
8
V
X
V
RL
V
16
Application Note
Trip
–
+
DD
/V
SS
15